This invention relates to fluid cylinders and, more specifically, to improved constructions for double rod ended fluid cylinders.
Prior art of possible relevance includes U.S. Pat. Nos. 2,983,256 issued May 9, 1961 to Seeloff; 3,307,484 issued Mar. 7, 1967 to Hammelmann; and 3,502,001 issued Mar. 24, 1970 to Moore.
The provision of an inexpensive, but reliable, double rod ended cylinder capable of employing fluid at high pressures has long been sought for a variety of uses. The principal difficulty in providing such a cylinder that is reliable and economic in construction is due to difficulty in obtaining precise concentricity of various parts. As is well known, double rod end cylinders require rod receiving openings in both ends of the cylinder housing and such openings must be aligned with each other and concentric with the cylinder bore. Slight deviations from concentricity can be accommodated through flexibility of seals employed, but when seal flexibility is relied upon, operating pressures must be similarly decreased if leakage is to be maintained at a predetermined minimum. Alternately, the stroke of the rod may be restricted to something less than the overall length of the housing so as to allow small deflections necessary to provide requisite sealing in the absence of good concentricity to occur and yet preclude binding of the rod in its housing bearings at both ends of its stroke. When this approach is employed, the resulting cylinders, of necessity, provide a considerably shorter stroke than what would be surmised from a casual inspection of the cylinder. Thus, space problems in use arise.
The last alternative is to fabricate the cylinders with exacting tolerances. Of course, this procedure is expensive and the resulting cylinders may be uneconomical for a large variety of uses.